1. Field of the Invention:
The present invention relates to a spacer suitable for use in attaching a packaged electronic component, such as an IC (Integrated Circuit) chip, onto a printed wiring board which has electronic circuits mounted thereon. The invention also relates to a printed circuit board that includes such a spacer mounted thereon and to electronic equipment including such a printed circuit board.
2. Description of the Related Art:
Japanese Patent Application Laid-open No. HEI 6-23276 (Patent Document 1), for example, discloses an IC package mounting structure which includes an insulating spacer, interposed between an IC package (circuit element) and a printed wiring board (circuit board), to conceal electrode pins exposed in a gap formed between the IC package and the circuit board so as to prevent dust or metal debris entering and accumulating in the gap, which can cause insulation faults and operation faults.
Conductive materials, such as metal debris, entering the gap between the IC package and the circuit board can cause a short circuit and subsequent disfunction of the IC package. In particular, such a short circuit occurring between electrode pins can even cause burnout. Further, nonconductive objects can also cause insulation faults if they enter the gap and are combined with moisture.
According to the technique of Patent Document 1, a spacer is attached to the circuit board before an IC package is mounted thereon, thereby preventing foreign objects entering the gap between the IC package and the circuit board.
[Patent Document 1] Japanese Patent Application Laid-open No. HEI 6-23276
However, when such a previous IC package mounting technique is applied to a BGA (Ball Grid Array), where IC packages are soldered onto a printed wiring board, the following problems are encountered:
(1) Since the spacer is required to be made from a material resistant to heat from soldering, the manufacturing cost of the spacer is increased;
In particular, from an environmental point of view, lead-free solder has recently become more and more common. Since such lead-free solder, in comparison with lead-containing solder, requires a high temperature for soldering, spacers need to be made from material with high heat-resistance.
(2) If a need arises to remove IC packages from the printed wiring board for any reason, the spacers attached thereto interfere with detachment of the IC packages.
For instance, during a process of blowing hot air to melt solder to separate an IC package from a wiring board, a spacer arranged therebetween obstructs the hot air sent to terminals between the IC package and the board, thereby making it difficult to detach the IC package from the wiring board.
In addition, if the material of the spacer is not resistant to heat from the hot air, the spacer can be welded to the printed wiring board or the IC package, thereby interfering with the detachment of the IC package.
(3) After attaching IC packages to a printed wiring board, if the board needs to be washed, the spacers make it difficult for cleaning fluid to reach soldered portions, thereby causing insufficient washing. On the other hand, once the cleaning fluid reaches the soldered portions, the spacer makes exit of the cleaning fluid difficult. That is, the spacer decreases the efficiency of washing the printed wiring board.
(4) From the viewpoint of efficient use of resources, such spacers are preferably recycled. At recycling, it is necessary to remove solder debris or flux adhered to the spacers at attachment or detachment of IC packages. Such removal requires complicated processes, which makes recycling of spacers difficult and increases costs.